<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    div {
        background-color: red;
        height: 100px;
        width: 25%;
        float: left;
      }
  </style>
</head>
<body>
  <script>
    for (let i = 1 ; i <= 16 ; i++) {
      const myDiv = document.createElement('div');
      document.body.appendChild(myDiv);
    }

    function random(number) {
      return Math.floor(Math.random() * number)
    }

    function changeColor() {
      const rndColor = 'rgb(' + random(255) + ',' + random(255) + ',' + random(255) + ')';
      return rndColor;
    }

    const divs = document.querySelectorAll('div');

    for (let i = 0 ; i < divs.length ; i++) {
      divs[i].onclick = function(e) {
        e.target.style.backgroundColor = changeColor();
      }
    }
  </script>
</body>
</html>